Means for preventing interference



Feb. 13, 1934. c s FRANKUN AL 1,946,680

I MEANS FOR PREVENTING INTERFERENCE Filed March 15, '1928 INVENTORS CH ES SFRANKLIN and. B R vylworr ATT RNEY Patented Feb. 13, 1934 UNITED STATES PATENT OFFICE MEANS FOR PREVENTING INTERFERENCE Application March 15,

1928, Serial No. 261,984,

and in Great Britain April 6, 1927 3 Claims.

This invention relates to ignition systems suitable for use in internal combustion engines, and has for its principal object to provide an ignition system by which interference with any radio receiving sets which may be placed in proximity thereto shall be reduced as much as possible.

As is well known, electric ignition systems on internal combustion engines generally cause more or less serious interference with wireless reception carried on in the neighborhood, the degree of interference varying with the type of wireless receiver, strength of incoming signal, wave length, type of ignition system and other iactors.

Such interference is especially serious when wireless reception is carried out in an aeroplane, where bad reception. conditions in the form of engine noise and \vindage already exist. Most aero engines are fitted with two sparking plugs per cylinder, and a separate magneto feeding each set of plugs. In addition there is usually a long high tension lead coming back from the main magneto distributor to a starting magneto which may also cause disturbance.

From the point of view of such interference, the magneto may be regarded as a spark trans mitter which is always in operation and always in close proximity to the wireless receiver, with the result that while the received strength of desired signals decreases as the receiving station gets further and further away from the source of the said desired signals, the strength of the interference remains always at a maximum.

According to this invention an electrical ignition system omprises one or more choke coils or inductances connected in series in the ignition sup-ply lead or leads to the insulated terminal or terminals of the sparking plug or plugs.

Such chokes or inductances should be constructed to have a low self capacity and should be mechanically robust.

The inductance of the choke should be such that the frequency of the oscillations produced when it is in circuit is not the same as that of the signals to be received, nor the same as that of any of the circuits of the receiver capable of being influenced directly by these oscillations.

In the case of magnetos which have a wipe or brush contact in the high tension distributor, interference can be abolished or minimized by the use of an inductance or choke coil connected in series between the insulated electrode of each sparking plug and the associated cable leading to the high tension distributor. If desired the chokes or inductances may be incorporated in the sparking plugs.

In the case of magnetos fitted with a so-called jump gap distributor, an additional choke is fitted between each distributor segment and the cable leading to the associated sparking plug. If desired the chokes adjacent the distributor of the magneto may be incorporated with the distributor casing.

The action of the chokes appears to be to convert the highly damped very high frequency impulses or oscillations which would exist without them, into oscillations of a definite frequency and of comparatively small damping. Such oscillations can be eliminated from a radio receiving set with comparative ease, provided that the frequency is not the same as that which is being received by l the receiver nor the same as that of any of the tuned circuits of the said receiver.

The invention is illustrated in the accompany ing drawing, in which Figure 1 shows in end view, Figure 2 in sectional elevation on the line X-X, Figure 1, and Figure 3 in bottom plan, one form of construction.

Referring to the drawing, a choke device comprises an insulated body 1 made, for example, of the material known under the registered trademark Bakelite, having an internally tapped tubular portion 2, adapted to receive a high tension magneto cable 3 (see Figure 2) which is held in position and to which electrical connection is made by means of a screwed piercing pin 4. Wound upon a wide groove 5 cut in the body 1 is a choke winding consisting, for example, of about 45 turns of insulated wire 11, the said winding being covered over by an insulating sleeve 6. At the end of the device remote from the cable 3 is a connection member 7 of brass or the like, formed with an eye 8 adapted to engage the stem of a sparking plug. The choke winding is connected in series between the piercing pin 4 and the eye 8, by means of pins 9 to which the ends of the said winding are soldered. 10 is an insulating plug which is screwed up against the end face of the member '7.

Having now particularly described our invention and the operation thereof, we claim:

1. A choke coil to be used in electrical systems operating adjacent other electrical devices, including a cylindrical insulating base member having a groove in the periphery of said base member, an inductance in said groove, a connector in each end of an opening through said base member, an insulating spacing member between said connectors, a contact member connecting each end of said inductance to one of said connectors, and a cylindrical insulating member surrounding said inductance and base member.

2. A choke coil to be used in electrical systems operating adjacent other electrical apparatus, including a non-conductive base member and a nonaxial opening through said base member, a metallic supporting connector retained by a shoulder in one end of said opening, an insulated conductor in the other end of said opening, a threaded spacin; member between said conductors, an inductance in a groove in the periphery of said base member, a connection between each end of said conductor and one of said connectors, and an insulating member surrounding said inductance.

3. A choke coil to be used in electrical systems operating adjacent radio apparatus, said choke coil having a predetermined inductance value whereby transient oscillations originating in the electrical systems would be converted into a narrow band of frequencies which are outside of the frequency band of any of the tuned circuits of the adjacent radio apparatus, comprising a cylindrical insulating base member having a groove in its periphery, said choke coil wound in the groove of said base member, a. connector in each end of the opening through said base member, an insulating spacing member between said connectors, a contact member connecting each end of said choke coil to one of the said conductors, and an insulating member surrounding said choke coil.

CHARLES SAMUEL FRANKLIN.

ARTHUR WILLIAM WHISTLECROF'I. 

